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Introduction to H.264 Video Standard Anurag Jain Texas Instruments.

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Presentation on theme: "Introduction to H.264 Video Standard Anurag Jain Texas Instruments."— Presentation transcript:

1 Introduction to H.264 Video Standard Anurag Jain Texas Instruments

2 H.264 Background  Jointly developed by ITU-T and MPEG.  Upto 50% more efficient at the same virtual quality compared to MPEG-4 ASP  Supports wide range of applications. (interlaced, progressive, low bit- rate, studio quality digital cinema etc).  Multiple profiles (Baseline, Main, Extended, High, FRExt).  Good results obtained from interoperability tests making it suitable for wide deployment in short span of time.

3 H.264 Encoder Block Diagram [Single Universal VLC and Context Adaptive VLC] OR [Context-Based Adaptive Binary Arithmetic Coding] Intra Prediction Modes 9 4x4 & 4 16x16 modes = 13 modes Seven block sizes and shapes Multiple reference picture selection 1/4-pel motion estimation accuracy Referenced B-frames Intra Inter _ Video Source Transform Bit Stream Out Quantized Transform Coefficients Motion Vectors + Predicted Frame Quantization Entropy Coding Motion Estimation Frame Store Motion Compensation Inverse Quantization Inverse Transform + Coding Control Loop Filter + Intra Prediction Integer 16-bit fixed point transform with no mismatch Quantization step more resolution for finer control of bit rate

4 Common elements with other standards  Macroblocks: 16x16 luma + 2 x 8x8 chroma samples  Input: association of luma and chroma and conventional block motion displacement  Motion vectors over picture boundaries  Block Transform  Variable block-size motion  I, P and B picture coding types Common Elements

5 High Level Coding Tools  Sequence and Picture Parameter Sets (SPS & PPS)  Picture Order Count (POC)  Decoded Picture Buffer (DPB)  Slice group map (FMO)  Multiple slices and arbitrary arrangements (ASO)  Supplemental Enhancement Information (SEI)  Hypothetical Reference Decoder (HRD)  Video Usability Information (VUI)

6  A coded sequence contains one or more access units  An access unit is a set of NAL units that contains all necessary information for decoding exactly one (primary) coded picture  A coded picture is divided into Slices (VLC NAL units)  A slice contains a slice header and a set of macroblocks  A macroblock contains a 16x16 luma block and two chroma blocks  An I-slice contains a set of INTRA-coded macroblocks  A P-slice contains a set of INTRA- and INTER-coded macroblocks  An IDR (instantaneous decoding refresh) picture contains only I-slices (SI-slices too in extended profile) High Level Tools: Coding Hierarchy

7  Level indicator  Profile constraint indicator  Sequence parameter set ID (0..31)  Picture order count type and infos  DPB (Decode Picture Buffer) info  Picture size  Frame/field coding flag  Method for vector derivation of B-direct mode  Frame cropping parameters  VUI_parameters (Annex E, Video usability information) Sequence Parameter Set

8 Picture Parameter Set  Picture parameter ID (0..255)  Sequence parameter ID (0..31)  Entropy coding mode flag (CABAC/CAVLC)  Slice POC info presence flag  Slice group map parameters  Max. number (1..16) of ref. frames used for decoding slices  Weighted prediction flags  Quantization scales (qp minus 26, range )  Chroma QP offset for loop-filter ( )  Slice loop-filter control flag (Alpha/Beta table offsets)  INTRA predication using pixels of INTER neighboring MBs?  Slice redundant pic. parameters presence flag

9  Starting macroblock address  Slice type (I, P, B, SI, SP )  Temporal reference (frame_num)  Picture parameter set ID (0..255)  Interlaced frame/field coding, top/bottom field indicators  IDR pictire ID (0,… 65536)  Slice POC parameters  Redundant picture count( , 0 for baseline)  B-slice temporal or spatial direct mode indicator  Max. number (1..32) of ref. pictures for decoding current slice  Reference picture reordering parameters (DPB)  Weighted prediction parameters  DPB marking parameters (e.g. short term, long term pred. Pics)  Slice delta QP ( )  SP switch flag and SP/SI slice QP  Loop-filter indicator (0: disabled, 1: enabled, 2: enabled but LP across slice Boundaries disabled)  Loop-filter alpha/beta table access offset (-6, +6)  Slice group change cycle (derives the No. of MBs in slice group 0) Slice Header

10 Slice Group Maps For error resilience

11 Ordering of Slices within Slice Groups

12 Low Level Coding Tools  Motion compensated prediction  Additional intra modes for spatial compensation  Transform: 4x4 Integer transform (Baseline, Main Profiles)  Transform: 8x8 Integer transform (High Profile)  Quantization: Scalar quantization  Entropy Coding : CABAC / CAVLC  In-loop deblocking filter

13 Enhanced MC (Inter Prediction)  Every macroblock can be split in one of 7 ways for improved motion estimation  Accuracy of motion compensation = 1/4 pixel  Up to 5 reference frames for SDTV L3  Weighted predictions  Reference B pictures  Trade off between accuracy and side information

14 B Slice - Direct Mode Direct mode  Forward / backward pair of bi-directional prediction  Prediction signal is calculated by a linear combination of two blocks that are determined by the forward and backward motion vectors pointing to two reference pictures.  Spatial Direct mode  Temporal Direct mode mvL0 = tb  mvCol / td mvL1 = – (td – tb)  mvCol / td where mvCol is a MV used in the co-located MB of the subsequent picture

15 B Slice : Multi-picture Reference Mode Generalized Bidirectional prediction  Multiple reference pictures mode  Two forward references : proper for a region just before scene change  Two backward references : proper for a region just after scene change traditional Bidirectional

16 H.264 Intra Prediction  4 modes for 16x16 intra prediction  9 modes for 4x4 blocks

17 Luma Sub-Pixel Interpolation

18 Chroma Sub-pel Calculation If (vx, vy) is luma vector, then xFracc = vx&0x7, yFracc = vy&0x7

19 Block Scanning Order in a MB One more extraction of correlation among sub-blocks

20  Integer 4x4 DCT approximation. 8x8  Cost of transformed differences (i.e. residual coefficients) for 4x4 block using 4 x 4 Hadamard-Transformation for INTRA_16x16 coded macroblocks.  Scalar quantization. Transform & Quant Hadamard 8x8 Luma-Chroma 4x4 Luma/Chroma AC All integers!

21  Deblocking filter  Frame / Field Adaptation  Picture Adaptive Frame Field (PicAFF).  Macroblock Adaptive Frame Field (MBAFF)  Field scan and zig-zag scan options Interlaced Coding Zig-zag Frame Scan Field Scan

22  Universal Variable Length Coding (UVLC) using Exp-Golomb codes.  Context Adaptive VLC (CAVLC)  Context Adaptive Binary Arithmetic Coding (CABAC) Entropy Coding

23 CAVLC TotalCoeff = 7 : # of non-zeros Trailing 1s = 2 : 1, -1 Sign Trail = 1 0 (reverse order) : minus, plus Levels = (reverse order) : 7 – 2 = 5 TotalZeros = 3 (# of zeros) RunsBefore = : 0 before -1, 2 before 1, and 0’s before 5 Zigzag order:

24 Exp Golomb Coding

25 Loop filter Check if the boundary is original to picture or blocking effects

26 Profiles and Tools

27 H.264 Profiles and Tools: Graphical Representation

28  Lossless representation  Allows more than 8-bits per sample (upto 12-bits)  Higher resolution for color representation (4:2:2, 4:4:4)  Source editing function like alpha blending  Very high bit-rates (often with constant quality)  Very high-resolution  Color space transformation (YCgCo, YCbCr, RGB)  RGB color representation  Adaptive block transform sizes  Quantization matrices FRExt: Fidelity Range Extension

29 Coding Efficiency

30 Comparision of Standards Feature/StandardMPEG-1MPEG-2MPEG-4 part 2 (visual) H.264/MPEG-4 part 10 Macroblock size16x1616x16 (frame mode) 16x8 (field mode) 16x16 Block Size8x8 16x16, 16x8, 8x816x16, 8x16, 16x8, 8x8, 4x8, 8x4, 4x4 Transform8x8 DCT 8x8 DCT/Wavelet 4x4, 8x8 Int DCT 4x4, 2x2 Hadamard QuantizationScalar quantization with step size of constant increment Vector quantization Scalar quantization with step size of increase at the rate of 12.5% Entropy codingVLC VLC, CAVLC, CABAC Motion Estimation & Compensation Yes Yes, more flexible Up to 16 MVs per MB Playback & Random Access Yes

31 Comparision of Standards (cont’d..) Feature/StandardMPEG-1MPEG-2 MPEG-4 part 2 (visual) H.264/MPEG-4 part 10 Pel accuracyInteger, ½-pel Integer, ½-pel, ¼-pel Integer, ½-pel, ¼-pel ProfilesNo583 Reference pictureone multiple Bidirectional prediction mode forward/backward forward/forward forward/backward backward/backward Picture TypesI, P, B, DI, P, B I, P, B, SP, SI Error robustnessSynchronization & concealment Data partitioning, FEC for important packet transmission Synchronization, Data partitioning, Header extension, Reversible VLCs Data partitioning, Parameter setting, Flexible macroblock ordering, Redundant slice, Switched slice Transmission rateUp to 1.5Mbps2-15Mbps64kbps - 2Mbps64kbps -150Mbps Compatibility with previous standards n/aYes No Encoder complexityLowMedium High

32 References –Related group MPEG website JVT website: ftp://ftp.imtc-files.org/jvt-expertsftp://ftp.imtc-files.org/jvt-experts –Test software H.264/AVC JM Software: –Test sequences ftp.tnt.uni-hannover.de/pub/jvt/sequences/

33 THANKS


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